1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to a liquid crystal display with liquid crystal (LC) material sealed between two substrates using a one drop fill (ODF) process.
2. Description of the Related Art
Liquid crystal display typically comprises two glass substrates oppositely positioned and a liquid crystal layer interposed therebetween. Specifically, the glass substrates are assembled by the following steps. First, an adhesive seal material is applied, usually by either silkscreening or screen printing. An opening is left in the seal for liquid crystal (LC) material injection in the subsequent process. After the adhesive is applied, spacers are provided on one of the substrates to maintain a precise cell gap (between 3-10 micrometers) between the two substrates. Typically, the spacers are formed by spraying glass or plastic beads on one of the substrates or by using resin to fabricate photo-spacers onto one of the substrates via the photolithography process. The substrates are then aligned and laminated by heat and pressure to complete the cross-linking of the polymer. After the assembling process is completed, the assembled glass substrates are cut into individual LCD cells. After the liquid crystal material is injected into the LCD cell by vacuum injection (vacuum injection method), the opening that was left open for this injection is sealed.
Conventionally, the opening sealing process is done in a chamber under pressure in order to squeeze the excess liquid crystal material from the LCD cell and bring the sealing resin into the opening of the LCD. Specifically, increasing the air pressure in the chamber creates a pressing force against the outer surfaces of the LCD cell, and the excess liquid crystal material will be forced out of the opening of the LCD before the sealing resin is applied. Furthermore, the pressed LCD cell will gradually restores its original shape when the chamber is brought back to atmospheric pressure; and hence, the sealing resin will be sucked into the opening of the LCD.
The one drop fill (ODF) process generally comprises the steps of applying an adhesive onto the entire periphery of the first substrate, dropping the liquid crystal material to the first substrate, superposing the second substrate upon the first substrate, and curing the adhesive.
In comparison with vacuum injection method used widely in manufacturing liquid crystal displays, the ODF process significantly reduce costs for manufacturing liquid crystal displays and improve productivity on a mass production basis because, firstly, it significantly reduces the amount of LC material to be used and, secondly, it decreases the time required for injecting LC material. Therefore, a strong demand exists for the use of the ODF process in manufacturing liquid crystal displays.
According to the ODF process, a predetermined quantity of LC material is dispensed on a substrate using a liquid crystal dispenser. However, a problem can arise in that the quantity of the LC material in the LCD cell can become excessive or insufficient because of the dispensing accuracy of the dispenser and variation of the cell gap defined between the substrates. A shortage of the quantity of the LC material in the LCD cell results in so-called voids observed in the LCD cell. Gravity mura (wide-area pixel defect) can be observed when the quantity of the LC material in the LCD cell is excessive. Any liquid crystal display having such problems of voids or gravity mura is regarded as defective.